big block cylinder head question

[496coronet]

Good evening! About 20 years ago I bought a 1972 Chrysler Newport with the plan that some day I'm going to rebuild the heavy-duty 230 casting 400. Some day is now here. It's got the 346 heads and I'm ok with that. KB 240 pistons hung on the factory rods on a steel 383 crank, all nicely balanced. Putting in the old-school P4452993 .474 cam. Yes, there are a bazillion other cam choices, but I love the idle of this one. Engine is going into my '67 R/T while the 440 is on the stand. Factory AFB 3426S carb. Headers. Manifold undecided; maybe stock iron 383 (so I can use the factory big block unsilenced) or Performer RPM. Time to do some bashing of the 18-spline and dana 60.
So before I buy all the engine parts I'll need without doing any research, I've got a couple of questions for you guys that know a thing or two about big block cylinder heads.
1. What is the valve guide boss diameter? The Lunati dual springs I spec's for the job have an inside diameter of 0.697" and I'd hate to have to cut off that guide boss.
2. Is it a good idea to use spring locators on the bottom? Not a "big" cam by any means but the locators (assuming they'll fit around the guide boss) just seem like a good idea.
2. What are the chances those original 346 heads have hardened exhaust seats?
It is a pleasure being on this forum!! Thank you for any and all help, comments, etc.
Kevin Pacholka

 

[pnora]

Good evening! About 20 years ago I bought a 1972 Chrysler Newport with the plan that some day I'm going to rebuild the heavy-duty 230 casting 400. Some day is now here. It's got the 346 heads and I'm ok with that. KB 240 pistons hung on the factory rods on a steel 383 crank, all nicely balanced. Putting in the old-school P4452993 .474 cam. Yes, there are a bazillion other cam choices, but I love the idle of this one. Engine is going into my '67 R/T while the 440 is on the stand. Factory AFB 3426S carb. Headers. Manifold undecided; maybe stock iron 383 (so I can use the factory big block unsilenced) or Performer RPM. Time to do some bashing of the 18-spline and dana 60.
So before I buy all the engine parts I'll need without doing any research, I've got a couple of questions for you guys that know a thing or two about big block cylinder heads.
1. What is the valve guide boss diameter? The Lunati dual springs I spec's for the job have an inside diameter of 0.697" and I'd hate to have to cut off that guide boss.
2. Is it a good idea to use spring locators on the bottom? Not a "big" cam by any means but the locators (assuming they'll fit around the guide boss) just seem like a good idea.
2. What are the chances those original 346 heads have hardened exhaust seats?
It is a pleasure being on this forum!! Thank you for any and all help, comments, etc.
Kevin Pacholka

I doubt you will need locators. Springs can be a problem. Inners can rub the guide. Back then we used to get the guides cut for proper seal fitment and the smaller seal would not get raked off the guide by the inner spring.

 

[496 polara]

That cam should not require double springs. Love that old school cam btw. One of my favorite mp cams.

 

[69Bee]

Guide diameter is large, 0.625" or larger. If you want Dual valve springs, cut them for positive seals for 0.562" OD guides. Should not need spring locators like pnora said, the head has good spring pockets. Depending on the OD of the spring, you might have to cut larger spring pockets. Now, as far as hardened valve seats, yes, they are "Flame Hardened" or "Induction Hardened. Problem is, after how many valve jobs do they reach a point where the hardness is affected. Put hardened exhaust seats in now, instead of the second time you go back in.

 

[496coronet]

Thank you, Thank you and Thank you. I appreciate the advice. Sounds like I should flush-cut the original guide bosses and install smaller (0.562") guides with the appropriate seal, allowing me to use my Lunati double springs. Yes this cam doesn't need the double spring, but I already have the springs new in the box. I was trying to save the original guide bosses but it makes no sense unless I'm using an umbrella seal with a single spring.
I'll skip the locators. Regarding the hardened seats, I'll think about what 69Bee is saying. The heads are cherry (engine was never disassembled before I came along - still had the original steel head gaskets) so unless my machinist says he's really got to grind a lot to seat the valves, I'm leaning towards holding off on the hardened seats.
Thanks again, Kevin

 

[Geoff 2]

I would get the guides machined for Viton valve seals. The good seals have a garter spring around the section that contacts the v/stem. You do not need dual springs, single pring with a damper is ok.

 

[496 polara]

I would be worried about wiping a lobe on a flat tappet cam with excessive spring pressure. Just my opinion.

 

[69Bee]

Thank you, Thank you and Thank you. I appreciate the advice. Sounds like I should flush-cut the original guide bosses and install smaller (0.562") guides with the appropriate seal, allowing me to use my Lunati double springs. Yes this cam doesn't need the double spring, but I already have the springs new in the box. I was trying to save the original guide bosses but it makes no sense unless I'm using an umbrella seal with a single spring.
I'll skip the locators. Regarding the hardened seats, I'll think about what 69Bee is saying. The heads are cherry (engine was never disassembled before I came along - still had the original steel head gaskets) so unless my machinist says he's really got to grind a lot to seat the valves, I'm leaning towards holding off on the hardened seats.
Thanks again, Kevin

No, take your heads to a machine shop and have them install 3/8"x 0.502" replacement guides, and cut the guide for positive seals. When people screw up the guides doing it incorrectly, I end up putting in 3/8"x 9/16" guides in to bring them back. I can go 3/4", but you will hit water, and I don't prefer to. A competent shop should be using a carbide cutter to cut all 3 or more angles at the same time. This way the seats are precise, and remove less material in the long run. Good luck...

 

[R/T Boy 67]

346 heads could have hard or soft seats depending on whether they were early or late castings. I had an early unmolested set that were soft.